Study on the Biodegradability of Hyperbranched Surfactant

Xuechuan Wang1, a, Yuqiao Fu1, b, Longfang Ren1, c and Taotao Qiang1, d

1Key Laboratory of Chemistry and Technology for Light Chemical Industry, Ministry of Education,

Shaanxi University of Science and Technology, Xi’an 710021, CHINA

a e-mail: wangxc@sust.edu.cn, b e-mail: fyuqiao@126.com,

c e-mail: renlf1010@163.com, d e-mail: qiangtaotao@sust.edu.cn

Key words: hyperbranched surfactant; biodegradability; COD30; respiratory curve.

Abstract. The methods of COD30 and respiratory curve were adopted to evaluate the

biodegradability of hyperbranched surfactant which was used as the substrate of microorganism.

The main results obtained by the method of respiratory curves were as follows. When the

concentration of substrate was 0~250mg/L, the respiratory curves of the substrate were above the

curve of endogenous, which showed that the substrate was easy to utilize by microorganism. The

main results obtained by the method of COD30 were as follows: when sludge concentration was

1000mg/L and pH was 7, the biodegradation rate of 200mg/L hyperbranched surfactant was 97.8%.

The main results obtained by the method of respiratory curves were as follows: When the

concentration of substrate was 200 mg/L, the utilization of the substrate by microorganism was the

most, respectively. Moreover, the effect of pH, inoculation amount and salinity on the

biodegradability of the substrate was obvious. Through experiments, the optimum conditions for the

substrate to be degraded could be listed as follows: pH was 8.5, salinity was 0.3% and the range of

inoculation amount was 3000mg/L.

Introduction

The use of green chemicals has been an important part of clean production in modern industry, as an

important parameter for evaluating the environmental friendliness of organic chemicals;

biodegradable property parameter has been widely acknowledged. A lot of people have studied the

biodegradability of surfactant. [1-4] Wang, et al. have emphasized the importance of surfactant

biodegradability study. [5] However, the study on the biodegradability of hyperbranched surfactant

was limited.

Hyperbranched polymers, a class of polymers characterized by a highly branched

macromolecular architecture and a large number of end groups, have attracted much attention in

recent years because of the expectation that their unique molecular shapes, branching patterns, and

surface functionalities may impart new, unusual properties.[6] First, As shown in Scheme 1 (a, b), a

series of hyperbranched poly (amine-ester) polyols (HPAEPS) were synthesized by the

polycondensation of N,N-diethylol-3-amine-methylpropionate [prepared by the Michael addition

reation of methyl acrylate (MA) with diethanolamine (DEA)] as an AB2-type monomer with

trimethylol propane (TMP) as the core moiety, proceeding in one-step procedure in the melt with

p-toluenesulfonic acid (p-TSA) as catalyst. [7] Then, as shown in Scheme 1 (c), HPAE was

modified by oleic acid to obtain a hyperbranched surfactant. (HPAE and oleic acid in the molar

ratio of 1:1) The biodegradability of the hyperbranched surfactant has been studied.

Advanced Materials Research Vols. 356-360 (2012) pp 223-227Online available since 2011/Oct/07 at www.scientific.net© (2012) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.356-360.223

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(a)

(b) (c)

Scheme 1. The steps involved in the synthesis of hyperbranched surfactant. (a) synthesis of AB2 type monomer; (b) synthesis of HPAE (AB2 monomer and TMP in the molar ratio of 3:1) (c) synthesis of hyperbranched surfactant (HPAE and oleic acid in the molar ratio of 1:1)

Experimental

Chemicals. C12H22O11 (purity 99%), (NH4)2FeSO4 (purity 99.5%) and K2Cr2O7 (purity 98.5%) were

purchased from Tianjin Chemical Reagent Co., Ltd, China. A mineral salt medium (MSM) used for

the growth of microorganisms contained (mg/L) NH4Cl, K2HPO4 FeSO4·7H2O 45, CaCl2 45,

MgSO4 30, ZnCl2 30 at pH 7.0. This MSM didn’t contain source of carbon and energy. All the

chemicals were of analytical grades and were purchased from Tianjin Chemical Reagent Co., Ltd,

China. The activated sludge sample was collected from the sludge compression workshop of the 3rd

Sewage Treatment Plant in Xi’an, China.

Microorganism Cultivation. Appropriate amount of collected activated sludge was transferred to a

culture flask filled with 2000mL of sterile MSM containing C12H22O11 as the sole source of carbon

and energy. The microorganism was incubated day by day until the microorganism characteristics

were detected as follows. The collected activated sludge became yellow flocculent sludge, the SV30

was about 30%, and the MLSS was about 3000mg/L, which indicated that the activity of

microorganism was good enough for the followed experiment of organic biodegradability

determination.

Evaluation of the Biodegradability of Hyperbranched Surfactant

The Biodegradability of Hyperbranched Surfactant. As presented by Kong et al. [8] and

Zhang, et al. [9], the methods of organic chemical biodegradability evaluation include Respiratory

curves, COD30, et al.

Respiratory Curves. Respiratory curve was mainly used to evaluate the initial adaptability of the

microorganism to the substrate.

COD30. COD30 was mainly used to evaluate the ultimate biodegradability of the substrate, which

reflected the maximal degree of substrate utilization by the microorganism.

224 Progress in Environmental Science and Engineering

Factors Affecting the Biodegradability of Hyperbranched Surfactant. The method of

respiratory curve was adopted to evaluate the affection of sludge concentration, pH and salinity on

the substrate biodegradation.

Results and discussion

The Biodegradability of Hyperbranched Surfactant

Fig. 1 The relationship Fig. 2 The relationship

between the substrate concentration between the substrate concentration

and biodegradability and biodegradability

Respiratory Curves. BOD of the different concentration substrates (50mg/L, 100mg/L,

150mg/L, 200mg/L and 250mg/L) was measured using BOD analyzer with other measurement

conditions as follows. pH at 7.0, 20˚C, prepared mineral salt medium (MSM), 1000mg/L fully

aerated fresh activated sludge. Moreover, The BOD of blank sample, whose substrate concentration

was 0 mg/L, was measured by BOD analyzer with the same other measurement conditions. During

each sample BOD measurement, the every day BOD value was recorded, and the respiratory curves

was obtained as Fig. 1.

Fig. 1 showed the substrate concentration had great influences on the substrate biodegradability.

Under the experimental conditions, the substrate respiratory curves were all above the endogenous

respiration curve which indicating that the tested different concentration of substrate has effect on

microorganism and could be largely degraded by the microorganism. When the concentration of the

substrate was 200mg/L, the influence of the substrate by microorganism was the most. The next are

250mg/L.

COD30. 250ml different concentration of the substrate (50mg/L, 100mg/L, 150mg/L, 200mg/L

and 250mg/L) were transferred to five conical flasks. Other test conditions were controlled as

follows. pH at 7.0, mineral salt medium (MSM) through adding appropriate content mineral salts in

the conical flasks, 1000mg/L fully aerated fresh activated sludge. The five conical flasks were then

putted in constant temperature shock incubator with the temperature 20˚C constantly. The test was

lasted 30 days. The COD of each sample was determined and recorded every 5 days. The COD30

curves were obtained as Fig. 2.

As shown in Fig. 2, in the condition of pH at 7.0, 20˚C, when the substrate concentration was in

the range of 50~250mg/L, the ultimate biodegradation rates were all above 90%. The

biodegradability of the substrate with the concentration of 200mg/L was the best and the ultimate

biodegradation rate was 97.8%.

Advanced Materials Research Vols. 356-360 225

Factors Affecting the Biodegradability of Hyperbranched Surfactant. Firstly, the substrate

biodegradability was determined at sludge concentration 500mg/L, 1000mg/L, 1500mg/L,

2000mg/L, 3000mg/L with other determination conditions as follows. 200mg/L substrate,

mentioned salt medium conditions, pH 7.0, and salinity 0%; Secondly, the substrate

biodegradability was determined at pH 6, 6.5, 7, 7.5, 8, 8.5with 200mg/L substrate, 3000mg/L

sludge concentration, 0% salinity and the same other determination conditions as before; Thirdly,

the substrate biodegradability was measured at salinity 0%, 0.1%, 0.3%, 0.5%, 0.7%, 0.9% with

200mg/L substrate, 3000mg/L sludge concentration and at pH 8.5, the same other determination

conditions as before.

Fig. 3 The relationship Fig. 4 The relationship

between sludge concentrations between pH and the substrate

and the substrate biodegradability biodegradability

Fig. 5 The relationship between salinity and the substrate biodegradability

Effect of Sludge concentration. As shown in Fig. 3. With the increase of inoculation amount,

the substrate biodegradability became better as the sludge concentration was among 500～

3000mg/L. The more the inoculation amount, the more the substrate degraded by microorganism.

When the inoculation concentration increased to 3000mg/L, the substrate biodegradation rate

increased.

Effect of pH. Fig. 4 showed that the hydrogen ion concentration of the culture medium greatly

influenced the substrate biodegradability. The reason was pH limited the activity of the

microorganism. Under the test conditions, the optimum pH for the substrate biodegraded was 8.5,

which indicated that strong alkaline medium had good influence on the biodegradability of the

substrate.

226 Progress in Environmental Science and Engineering

Effect of Salinity. Fig. 5 showed the salinity of the culture medium had great influences on the

substrate biodegradability. During the process of microorganism using the substrate as the sole

source of carbon, appropriate mineral salts should be provided for the normal activity of the

microorganism. Under too high or too low salinity, the microorganism cells would dehydrate or

hydrate and the microorganism activity would be inhibited as a result of the inapplicable osmotic

pressure environment. Under the test conditions, when the additional NaCl was in the range of

0%~0.3%, the substrate biodegradability became better with the increase of salinity. However, when

the additional NaCl was above 0.3%, the substrate biodegradability became worse with the increase

of salinity. The optimum salinity for the substrate biodegraded by the microorganism was 0.3%

additional NaCl.

Conclusions

(1) Hyperbranched surfactant was used as the substrate of microorganism, when sludge

concentration was 200mg/L, pH was 7 and with no additional NaCl, the biodegradation rate of

200mg/L hyperbranched surfactant was 97.8%.

(2) The methods of respiratory curve showed that the substrate has inhabiting effect on

microorganism, and could easily biodegradation by microorganism. The result of the method of

Respiratory Curve was consistent with that of COD30.

(3) Moreover, as indicated in the respiratory curves, the effect of sludge concentration, pH, salinity

and co-metabolism on the biodegradability of the substrate was obvious.

(4) Under the experimental conditions, when the concentration of the substrate was 200mg/L, the

sludge concentration was 3000mg/L, pH was 8.5 and salinity was 0.3%, the biodegradability of

the substrate was the best.

Acknowledgements

This research was supported by National Natural Science Foundation of China (20876090);

Scientific research team Shaanxi University of Science & Technology (TD09-04) and the Graduate

Innovation Fund of Shaanxi University of Science and Technology.

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Advanced Materials Research Vols. 356-360 227

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